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Calculate Electric Field in Medium

  1. Dec 7, 2008 #1
    Hello all! I'm studying for my final, and I'm trying to figure out my teacher's method for the following problem. Could you help me out?

    A plane wave is propagating in free space with a frequency of 10 GHz. The amplitude of the electric field in the x-direction is Ex = 2 V m-1.
    (ii) Find the magnitude of electric and magnetic field if the plane wave is transmitted through a medium with relative permittivity .


    She then goes on to say that you simply need to find the impedance of the material and set H=E/impedance. I realize that this is a true ratio, but shouldn't we have to calculate to magnitude of E in the medium? She uses the value of E in free space, which I think is wrong.

    Her answers: E=2 V/m H=11.86 mA/m

    Thanks in advance!
     
  2. jcsd
  3. Dec 10, 2008 #2

    olgranpappy

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    relative permittivity... what? was there supposed to be a number after the word "permittivity" and before the period?

     
  4. Dec 11, 2008 #3

    Andy Resnick

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    I really hope there was more to the question than what you typed- as it stands, it's awful.

    First, I wonder if the instructor is being cute- the *electric* field in a medium is the same as the electric field in empty space: it is the *displacement* field that is different in matter.

    as for the magnetic field, here's how to get there: the magnitude of the magnetic induction B is E/c (c is the speed of light), and the permeability is found from the relationship between the permittivity, permeability, and c:

    http://hyperphysics.phy-astr.gsu.edu/Hbase/electric/elefie.html

    I didn't run the number to see if that's correct. I bet writing all that down analytically, many extraneous factors cancel which will simplify the calculation.
     
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